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arXiv 0710.4606math.CO
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m-凸多边形族:m = 2

Families of m-convex polygons: m = 2

W. R. G. James, I. Jensen, A. J. Guttmann

摘要:

如果多边形的周长与其最小外接矩形的周长相差其“凸指数”$m$的两倍,则多边形被描述为几乎凸的。这种多边形被称为\emph{$m$-convex}多边形,其特征在于在侧面具有多达$m$的凹痕。我们使用一个“分而治之”的方法,因式分解2-凸多边形延长线沿其缩进的基础。然后,我们使用的容斥原理,Hadamard产品和扩展已知的方法来获得每种情况下的生成函数。

英文摘要:

Polygons are described as almost-convex if their perimeter differs from the perimeter of their minimum bounding rectangle by twice their `concavity index', $m$. Such polygons are called \emph{$m$-convex} polygons and are characterised by having up to $m$ indentations in the side. We use a `divide and conquer' approach, factorising 2-convex polygons by extending a line along the base of its indents. We then use the inclusion-exclusion principle, the Hadamard product and extensions to known methods to derive the generating functions for each case.

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